Auxiliary power units (“APU”) are used in aircraft to provide electrical power and compressed air to various aircraft systems and components. When an aircraft is on the ground, its main source of electrical power and cabin conditioning comes from the APU. In particular, the APU can power the environmental control systems, air drive hydraulic pumps, and the starters for the engines. When an aircraft is in flight, the APU may provide pneumatic and/or electric power to the aircraft.
Typically, APUs are located in the aft section of the aircraft, at or near the tailcone section and include inlet and exhaust ducting that exit through an opening, or cut-out, in the aircraft fuselage to allow sufficient air flow through to the APU. For aircraft on which APUs operate during flight, an inlet air door is typically provided to protect the APU from foreign object damage when not in use and/or during ground movement, and to maximize airflow into the APU when performance or oil cooling at altitude is required. Thus, when the APU is running, either on the ground or in flight, the inlet air door is in an open position.
During in-flight operations of the APU, there is a low pressure wake formation on the backside of the open inlet door, which can create relatively high drag loads. These high drag loads may also induce undesirable amounts of vibration on the door, which can have deleterious structural impact and may reduce over inlet door lifetime.
Hence, there is a need for an APU inlet door that, when open, does not exhibit undesirably high drag loads and/or does not have undesirable amounts of vibration induced therein and/or improves overall inlet door lifetime. The present invention addresses one or more of these needs.